1. Technical Field
The present invention relates to a resistive touch screen.
2. Description of the Related Art
With the development of the mobile communication technology, user terminals such cellular phones, PDAs, navigations can serve as a display unit that simply displays character information as well serve as a unit for providing various and complex multi-media such as audio, moving picture, radio internet web browser, etc. Recently, a demand for implementing a larger display screen within a terminal of a limited size has been increasingly expanded, such that a display scheme using a touch screen has been greatly in the limelight. The touch screen has an advantage of saving a space by integrating a screen and a coordinate input unit, as compared to a key input scheme according to a prior art.
A type of current mainly used touch screen is largely classified into two schemes.
First, in the capacitive touch screen, an upper substrate on which a first electrode pattern is formed having first directionality and a lower substrate on which a second electrode pattern having second directionality is formed are spaced apart from each other and an insulator is inserted between the first electrode pattern and the second electrode pattern to prevent them from contacting each other.
The capacitive touch screen measures a change in capacitance generated in the first electrode pattern and the second electrode pattern when input units touch the touch screen, thereby calculating coordinates of touched points.
The resistive touch screen is a type where an upper substrate on which an upper resistive film is formed and a lower resistive film is formed may be spaced apart from each other by a spacer and may be disposed to contact each other by an external pressure. The resistive touch screen depends on a scheme where when the upper substrate on which the upper resistive film is formed is pressed by input units, for example, fingers, pen, and so on, the upper/lower resistive films are conducted to each other and a controller recognizes the change in voltage according to the change in resistance value at the pressed point in order to recognize the touched coordinates.
The resistive touch screen generally includes a window formed on the upper substrate. Since the touch screen is coupled with a display device, a predetermined strength of window should be used to protect the touch screen.
Further, the resistive touch screen includes a covering film formed on the lower surface of the window in order to prevent electrode wirings made of an opaque material from being recognized from the outside. Meanwhile, the window formed with the covering film is bonded to the resistive touch screen by using an optical clear adhesive (OCA).
In this case, the optical clear adhesive (OCA), which is a transparent resin adhesive, has elastic force buffering external impact. Therefore, when the optical clear adhesive has a predetermined thickness or more, several problems occur. Generally, the upper resistive film and the lower resistive film contact each other due to the warpage of the upper substrate by the external pressure, such that they are conducted to each other. However, excessive pressure loads are required so as to generate touch signals that represent the generation of the external pressure when the optical clear adhesive has a predetermined thickness or more, such that touch sensitivity is degraded (that is, even though a user applies external pressure, touch signals are not generated due to low pressure loads). Therefore, this causes the trouble that the user should touch the window several times or more.
When the covering film is formed on the lower surface of the window, the thickness of the optical clear adhesive is further increased due to the thickness of the covering film, such that the foregoing problems are more serious. Therefore, research for improving the foregoing problems has been conducted.